While the present invention finds particular usefulness in the oil industry, it has particular application in other hostile pressure and temperature environments where size of the transducer and accuracy of the measurements are important. In an oil well pressure transducer, it is common to size a unit to go into a small diameter metal pressure housing for measurement of pressures up to 20,000 psi and even more and which can be subjected to downhole temperatures up to 400.degree. F. or more. The pressure housing must have a wall thickness sufficient to withstand the downhole pressures so that the O.D. of the internal pressure transducer is in the neighborhood of one inch. In addition to pressure and temperatures, the unit is subjected to rough treatment.
A downhole oil well pressure gauge can be transported by a wireline, cable or pipe string to one or more levels of interest in a well bore where both temperature and pressure are sensed over a period of time. Typically, pressure measurements are repeatedly sampled and recorded over a period of time at a sampling rate determined by down hole electronics and may be stored in a downhole memory for subsequent replay or sent to the surface for analysis. Alternately, sometimes gauges are attached to production strings or other downhole equipment for extended periods of time or "permanently".
In U.S. Pat. No. 5,207,767 and elsewhere, a capacitance type pressure transducer utilizes spaced apart capacitor plates on spaced apart base members to define two capacitances which dependently vary as one of the base members is torqued about a torque axis relative to the other base member. In some instances, various factors can cause the base members to be displaced relative to one another and produce potentially inaccurate measurements. The present invention provides a system for compensation of unintended shifting or displacement of base members relative to one another.